1. Field of the Invention
The present invention relates to an apparatus using plasma, and more particularly, to an ion beam apparatus having a plasma sheath controller and a semiconductor surface treatment apparatus employing the same.
2. Description of the Related Art
Semiconductor manufacturing apparatuses using plasma are widely used, for example, a plasma etcher, a plasma enhanced chemical vapor deposition (PECVD) apparatus, a surface treatment apparatus for metal or polymer, a synthesizing apparatus for new materials, an adhesion apparatus for different thin films, and so on. The semiconductor manufacturing apparatuses using plasma may include an ion beam apparatus.
FIG. 1 is a partial cross-sectional view of a conventional ion beam apparatus.
Referring to FIG. 1, the conventional ion beam apparatus includes first and second ion extraction grids 15 and 17 disposed at one surface of a plasma chamber (not shown). The ion extraction grids 15 and 17 have aligned ion extraction apertures 16. A positive voltage is applied to the first ion extraction grid 15. A negative voltage is applied to the second ion extraction grid 17. The second ion extraction grid 17 may be grounded.
The plasma chamber functions to generate plasma 11. Generally, a plasma sheath 13 is formed between the plasma 11 and an object opposite thereto. In this case, a plasma surface 12 exists at a position spaced apart from the opposite object by a thickness of the plasma sheath 13. Therefore, the plasma sheath 13 is formed between the plasma 11 and the first ion extraction grid 15.
The ion extraction grids 15 and 17 extract ions from the plasma 11 to discharge the ions via the ion extraction apertures 16. The extracted ions are accelerated in the form of an ion beam 19 while the ions pass through the ion extraction apertures 16.
Generally, an increase in density of the plasma 11 or expansion of the ion extraction apertures 16 is advantageous to an increase of ion flux of the ion beam 19. When the ion extraction apertures 16 have a diameter much smaller than the thickness of the plasma sheath 13, the plasma surface 12 is formed parallel to a surface of the first ion extraction grid 15. However, the higher the density of the plasma 11, the smaller the thickness of the plasma sheath 13.
Further, when the density of the plasma 11 is increased more, the plasma sheath 13 is formed along the ion extraction apertures 16. That is, the plasma 11 bows outward into the ion extraction apertures 16. In this case, the plasma surface 12 assumes a periodic curved/spherical form into the ion beam pathways through the ion extraction apertures 16.
The disadvantage of this deformation of the plasma surface is that the ions in the plasma 11 are extracted in a direction perpendicular to the plasma surface 12. Therefore, the ions extracted from the curved plasma surface 12 collide with the ion extraction grids 15 and 17. As a result, the ion flux of the ion beam 19 is somewhat reduced. This detrimental effect becomes even more pronounced as the density of the plasma 11 (e.g. the energy supplied to the plasma) is increased. It therefore becomes impossible to obtain high ion flux of the ion beam 19.
Semiconductor manufacturing apparatus using plasma is disclosed in U.S. Pat. No. 4,450,031, entitled “Ion Shower Apparatus,” filed by Ono, et al. According to Ono, et al., an ion shower apparatus including a shield grid and an ion extraction grid is provided. However, an ion beam apparatus capable of increasing ion flux is still required.
Accordingly, the need remains for methods of improving the ion flux of an ion beam.